This invention relates generally to machine vision systems for semiconductor chip bonding/attaching devices. More specifically, the present invention relates to an apparatus for imaging a bonding tool that takes into account system changes due to temperature and other nonrandom systemic effects.
Semiconductor devices, such as integrated circuit chips, are electrically connected to leads on a lead frame by a process known as wire bonding. The wire bonding operation involves placing and connecting a wire to electrically connect a pad residing on a die (semiconductor chip) to a lead in a lead frame. Once all the pads and leads on the chip and lead frame have been wire bonded, it can be packaged, often in ceramic or plastic, to form an integrated circuit device. In a typical application, a die or chip may have hundreds or thousands of pads and leads that need to be connected.
There are many types of wire bonding equipment. Some use thermal bonding, some use ultra-sonic bonding and some use a combination of both. Prior to bonding, vision systems or image processing systems (systems that capture images, digitize them and use a computer to perform image analysis) are used on wire bonding machines to align devices and guide the machine for correct bonding placement.
In conventional systems, post attach inspection is used to determine if changes in bonding tool position are necessary to effect proper wire bonds. As-such, these conventional systems can only compensate for improper wire bonds after such improper wire bonds are made, thereby negatively effecting device yield. These conventional systems have additional drawbacks in that they are unable to easily compensate for variations in the system due to thermal changes, for example, requiring periodic checking of completed devices further impacting device yield and negatively impacting manufacturing time.
In view of the shortcomings of the prior art, it is an object of the present invention to provide a vision system that takes into account variations due to temperature changes and other nonrandom systemic effects.
The present invention is a vision system for use with a bonding tool. The system comprises a cornercube offset tool having a plurality of internal reflection surfaces, and located below a vision plane of the bonding tool; and an optical detector to receive an indirect image of the bonding tool through the cornercube offset tool.
According to another aspect of the invention, the vertex of the cornercube offset tool is located at a position about midway between an optical axis of the optical detector and an optical axis of the bonding tool.
According to still another aspect of the invention, the focal plane of the bonder""s vision system is positioned above the cornercube offset tool.
According to yet another aspect of the present invention, the system includes a single lens positioned between the cornercube offset tool, and i) the optical detector and ii) the bonding tool.
According to still another aspect of the present invention, the system includes a first lens positioned between the optical detector and the cornercube offset tool and a second lens positioned between the bonding tool and the cornercube offset tool.
According to a further aspect of the present invention, the first lens and the second lens are located below the image plane.
According to yet a further aspect of the present invention, the angle between adjacent internal reflective surfaces of the cornercube offset tool is about 90xc2x0.
According to yet another aspect of the present invention, the angle between each of the internal reflective surfaces and the top surface of the cornercube offset tool is about 45xc2x0.
According to still another aspect of the invention, the optical detector is a CCD camera.
According to yet another aspect of the invention, the optical detector is a CMOS imager.
According to a further aspect of the invention, the optical detector is a Position Sensitive Detector (PSD).
According to an exemplary method of the present invention, a cornercube offset tool is positioned below a vision plane of the bonding tool; a lens is positioned between i) the bonding tool and the cornercube offset tool and ii) between an optical input device and the cornercube offset tool; and the bonding tool is viewed through the cornercube offset tool and the lens.
These and other aspects of the invention are set forth below with reference to the drawings and the description of exemplary embodiments of the invention.